The present invention relates to a method for determining the rolling force in a rolling stand, as well as to a rolling stand.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
U.S. Pat. No. 3,861,187 discloses a rolling stand for rolling rod-shaped or tubular material, with three rollers which are arranged in a star configuration about the longitudinal axis of the rolling stock. The roller journals disposed at the ends of at least one of the three rollers are eccentrically supported in respective eccentric bushings which have an inner, circular opening in which the radial bearing, preferably a roller bearing, of the roller journal is placed. The circular outer circumference of the eccentric bushing is supported in the housing of the rolling stand. The eccentricity of the eccentric bushing is due to the fact that the circle formed by the interior surface of the eccentric bushing and the circle formed by the exterior surface of the bushing are not coaxially aligned. Further described in U.S. Pat. No. 3,861,187 is the use of such roller design for adjusting the rollers in a rolling stand, e.g. for moving the rollers toward the rolling stock.
U.S. Pat. No. 3,861,187 further describes an adjusting mechanism for moving the eccentric bushing into a desired rotational position relative to the housing. A rotary motion of an adjusting shaft having an adjusting ring is transmitted to the eccentric bushing via an adjusting pin disposed on a rotatable adjusting spindle and a transfer lever which is flexible connected both with the adjusting ring and the eccentric bushing. Alternatively, a threaded spindle which is stationarily supported in the axial direction and on which a threaded bushing moves in the axial direction, can be used. The threaded bushing is connected with the adjusting ring via an articulated joint, with the adjusting ring encompassing a cup-shaped projection of the eccentric bushing and being non-rotatably connected with the eccentric bushing through a tight-fitting spring. These adjusting mechanisms enable rotation of the eccentric bushing relative to the housing in which the bushing is supported. The eccentric bushing can be held in the desired set position by blocking rotation of the threaded spindle. As a result, the radial spacing or gap between the rollers in a rolling stand can be adjusted for changing the diameter of the finished rolling stock and/or for compensating temperature-induced changes in the dimensions of the rolling stock or wear of the rollers.
U.S. Pat. No. 3,861,187 further discloses the support of the eccentric bushing in the housing by a friction bearing, i.e., the exterior surface of the eccentric sleeve slides on a surface of the housing when the eccentric bushing is adjusted. The gap can therefore only be adjusted when rolling stock is absent from the rolling stand. Otherwise, the eccentric bushing is subjected to the rolling force, which increases the tangential sliding friction forces between the housing of the rolling stand and the eccentric sleeve.
U.S. Pat. No. 6,041,635 discloses a different approach for adjusting the rollers of a rolling stand for rolling rod-shaped or tubular stock. The rollers are supported in stirrup-shaped brackets movable inside the frame along a longitudinal axis which is perpendicular to the rolling axis. The brackets are moved by hydraulic cylinders, wherein the piston ends can cooperate with the brackets and adjust the rollers by moving the brackets with the piston. The rolling force may then be determined by measuring the hydraulic pressure applied to the hydraulic cylinder.
However, adjusting the rollers with hydraulic cylinders has significant disadvantages:
If the hydraulic cylinders are part of an exchangeable rolling stand, i.e., if the hydraulic cylinders do not remain with the rolling mill when the rolling stand is changed (e.g., when changing product dimensions or gauge), then the feed line to each cylinder arranged in the rolling stand must be connected by way of a releasable hydraulic coupling. This is technically complex and can make a trouble-free operation of such rolling mill more difficult.
Conversely, if the hydraulic cylinders are fixedly installed in the rolling mill and therefore remain in the rolling mill when the rolling stand is changed, then several significant disadvantages result:                The rolling forces are not absorbed in the rolling stand itself, but in the support bearings of the hydraulic cylinders and are therefore transmitted to the steel frame of the rolling mill, requiring a massive and therefore rather expensive steel frame.        Removing the rolling stands from the rolling mill also increases the complexity in the construction and design, because of the hydraulic cylinders are arranged in a star pattern around the rolling access, so that the rolling stands can no longer be pulled out perpendicular to the rolling axis.        When the rolling stands are not installed in the rolling mill, the so-called rolling gauge defined by the three cooperating rollers cannot be controlled, because the components that determine the accuracy, namely the hydraulic cylinders, are located in the rolling mill. However, if the rolling stands are installed in the rolling mill, then the gauge can also not be controlled due to the lack of access.        
Adjusting the rollers in opposition to the rolling force with hydraulic cylinders is extremely expensive.
The system does not have an inherent fail-safe function, so that a hydraulic failure halts the rolling process.
It would therefore be desirable and advantageous to provide an improved method and system for measuring the applied rolling force in the presence of rolling stock, which obviates prior art shortcomings and is able to specifically adjust the rollers during the rolling process in the presence of the rolling force.